Method of making a dental appliance

ABSTRACT

A dental model formed from an impression taken from a patient&#39;&#39;s mouth is provided with anchoring wires at prescribed locations and then supported in a molding machine. The model is isolated or masked by surrounding it with small pellets of lead or other relatively dense material. An acrylic material in liquid form, a major constituent of which is methyl methacrylate, is applied to a selected portion of each wire, usually within the periphery of the model. Immediately thereafter a preheated sheet of thermoplastic material, a major constituent of which is methyl methacrylate, is applied to the model and shaped to conform thereto in a manner such that the selected portions of the anchoring wires are embedded in the plastic material. Upon cooling the resulting product, known as a retainer, is separated from the model.

United States Patent 1191 Breads 1 Oct. 30, 1973 METHOD OF MAKING ADENT-AL Primary ExaminerLo uis G. Mancene APPLIANCE AssistantExaminer-J. O. Lever [75] Inventor: Peter R. Breads, Buffalo, NY. Anomeycomad Christel et [73] Assignee: Great Lakes Orthodontic [57] ABSTRACTLaboratory lnc-iBuffaioiN-Y- A dental model formed from an impressiontaken [22] Filed; 06L 26,1972 from a patients mouth is provided withanchoring wires at prescribed locations and then supported in a l PP N05300,881 molding machine. The model is isolated or masked by surroundingit with small pellets of lead or other rela- 52 us. c1. 32/2 iiveiydense material acrylic material iii liquid 51 Int. Cl. A61c 13/00 form,a major Consiiiueiii of which is methyl 58 Field of Search 32/2, 13, 14B, 14 c iyiaie is applied to a Selected Portion of each Wire usuallywithin the periphery of the model. Immedi- [56] References Cited atelyrthereafter a preheated sheet of thermoplastic UNITED STATES PATENTSmaterial, a major constituent of which is methyl meth- I acrylate, isapplied to the model and shaped to con- 3,259,129 7/1966 Tepper 32 14 Bform thereto in a manner Such that the Selected pop 'tions of'theanchoring wires are embedded in the plas- Buhler 32/2 tic material. Uponcooling the resulting product, known as a retainer, is separated fromthe model.

12 Claims, 7 Drawing Figures One area of use of the present invention isin manufacturing dental and orthodontic appliances of the type having aplastic body portion from which anchoring wires extend although theprinciples of the invention can be variously applied. Appliances of thistype include a plastic body portion shaped to fit a portion of apatients mouth'such as the palate, andwires secured at one end to thebody' portion and extending therefrom and shaped to engage the patientsteeth.

In making such devices there have been problems adequately securing thewires to the body portion, and one solution of the prior art is toposition the ends of the wires between laminations of the plastic bodybefore heatis applied to mold the plastic to the desired shape.Usually'the ends of the wire are first cemented to one lamination beforethe other is placed on it. This procedure is relatively time consumingand requires a relatively thick plastic body portion which affects thecost of the appliance as well as comfort of the patient wearing theappliance.

SUMMARY OF THE INVENTION ltis, therefore, .an object of thisinvention-to provide anew and improved method of making a dentalappliance of the type having a plastic body portion from whichauxiliaries such as anchoring members extend.

It is a further object of this invention to provide such a methodwhereby ends of auxiliaries such as anchoring 'members are embedded in aunitary plastic body portion.

It is a further object of this invention to provide such a methodwherein a dental model is supported during moldingin a new and improvedmanner.

of which is methyl methac rylate, is applied to a selected portion ofthe anchoring member. Preheated thermoplastic material is applied to themodel and to the liquid coated portion of the anchoring member, and theplas tic is shaped to conform .to the model in a manner whereby theselected portion of the anchoring member is embedded in the plasticmaterial. The model is supported during molding by surrounding portionsthereof not to receive plastic by relatively small pellets of lead orsimilar dense material. After molding and cooling the resulting productis separated from the model.

The foregoing and additional advantages and characterizing features ofthe present invention will become clearly apparent upon a reading of theensuing detailed description together with the including drawingwherein;

BRIEF DESCRIPTION OF THE DRAWING FIGURES FIG. 1 isa fragmentaryelevational view, partly in section, of one form of apparatus used inperforming the method of the present invention;

FIG. 2 is a fragmentary top plan view of the apparatus of FIG. 1;

- FIG. 3 is a view similar to FIG. 2 and showing one step in the methodof the present invention;

FIG. 4 is a fragmentary sectional view of the appara ms of FIG. 1showing another step in the method of the present invention;

FIG. 5 is a perspective view of a dental appliance made by the method ofthe present invention;

FIG. 6 is a sectional view taken about on line 66 of FIG. 3; and

FIG. 7 is a sectional view taken about on line 7-7 of FIG. 5.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT A preferred form ofapparatus used in performing the method of the present invention isillustrated in FIG. 1.

V The apparatus or machine 10 is operated, briefly, to

heat preformed thermoplastic sheets or blanks to a soft state, placethem over a model or form, and then apply air pressure to form theplastic to the contour of the model. Machine 10 includes, briefly, acup-shaped receptacle 12 provided in the top surface of the body ofmachine 10 which receptacle is of a size sufficient to accommodatevarious sizes of dental models. A passage 14 connects receptacle 12 witha chamber (not shown) in device 10 for conducting air during the formingoperationLMachine 10 further comprises a component 16 including apressure chamber and a holder or frame 17 for holding blanks or sheetsof thermoplastic material to be used in the method of the presentinvention. Component 16 is pivotally connected to a bracket 18 mountedon machine 10 whereby it can be moved from the position shown in FIG. 1to a forming position placing a plastic blank over and onto the model aswill be described in detail presently. Machine. 10 further-comprises. aheater. 20 in the form of a heater lamp for radiating heat ontotheplasticblank held bycomponent l6.

Lamp 20 is swingably mounted on machine 10 so that it can be placed overthe plastic blank held in component 16 and then moved outof the way toallow component 16 to be pivoted to a forming position. Machine 10 isprovided with a control for regulating the operating pressure togetherwith appropriate pressure indicators. A machine similar to that shown inFIG. 1 is available under the commercial designation'BlOSTAR Dental'Molding Machine from Great Lakes Orthodontic Laboratory, lnc.,Buffalo, New York.

The method of the present invention is begun by providing a dental model24 formed from an impression taken from the mouth of the patient. Model24, also known in the art as a study model, is formed according toconventional procedures which are readily known to those skilled in theart so that a detailed description thereof is believed to beunnecessary. Suffice it to say, the dentist or orthodontist takies animpression of a patients teeth by having the patient bite into asuitable material capable of retaining an impression and then thismaterial is used as a mold to form model 24 of plaster or equivalentmaterial. Model 24 thus provides a facsimile of the upper or lower jawof a patient including front teeth 26, side teeth or molars 27 and apalatal surface portion 28 as shown in FIG. 2. It has been foundadvantageous to dampen the model and apply separating medium to thelinqual surface thereof and to the palatal surface.

The next step in the method of the present invention is positioningauxiliaries or accessories such as anchoring members on model 24. Inparticular, an anchoring member 30 in the form of a wire is bent orformed according to specifications provided by the dentist ororthodontist and is positioned on the front part of model 24 in a mannersuch that a portion of wire 30 is on the facial surface or outerperipheral surface of model 24 and portions 32 of wire 30 are within theperiphery of model 24. In particular, the portions 32 extend inwardly ofthe teeth and are adjacent the palatal portion 28 of the model. In thepresent example, two additional anchoring members or wires 33 are positioned on the opposite side portions of model 24, and each wire 33 has aportion 34 located adacent the palatal portion 28 of model 24. Theanchoring members or wires 30, 33 are ofa resilient material, preferablystainless steel. Wires 30, 33 are held in place by applying asbestos ora sticky wax substance over portions of the wires and the buccal surfaceor outer peripheral surface of model 24. The wire portions 32, 34adjacent palatal portion 28 of model 24 are relatively close to palatalportion 28, often being in contact therewith.

Model 24 is supported during the remaining operations performed thereon,and in the present instance model 24 is placed in and supported byreceptacle 12 of machine so that the occlusal/incisal edge of model 24is flush with or slightly above the top edge or surface of cup 12.According to the presentinvention, the region of receptacle 12 notoccupied by model 24 is filled by relatively small-sized pellets 38 ofrelatively dense material, preferably lead, to isolate model 24. Pellets38 are poured up to the top labial edge of the teeth of model 24 so asto be against the surfaces of model 24 which are not to receive plastic.In particular, pellets 38 serve to surround and support irregular shapesor surfaces which are encountered with model 24 and thereby serve tomask or isolate model 24 in receptacle, 12. The use of pellets 38protects the areas or surfaces of model 24 that are not to be coveredwith plastic during the forming operation, such as the undercuts in thelabial and buccal portions of the model. This, in turn, enables model 24to be removed from the plastic later on in a relatively easy manner.Overdrawing and undesirable thinning of the plastic from model 24 alsois prevented. Pellets 38 can be provided up to a level adjacent theincisal edge of the teeth of model 24 so that the teeth do not becomesurrounded by the plastic material in the forming operation. While leadis preferred, pellets 38 can be of any other material having sufficientdensity so as not to be damaged under the temperature and pressurecondition of the method of this invention whereby they can be usedrepeatedly.

The next step in the method of the present invention is heating a blank40 of thermoplastic material. The thermoplastic material used in themethod of the present invention is of the acrylic type having methylmethacrylate as a major constituent thereof. Blank 40 is positioned incomponent 16 of machine 10 and held therein by frame 17, and lamp 20 isswung into position over component 16 and operated at the requiredheating conditions. The heater 20 is operated at a maximum of 250 watts,and by way of example when thermoplastic blank or sheet 40 has athickness in the range of 1.5 to 2.0 millimeters, a heating time ofabout 60 seconds is required. In many instances visual control ofheating time is possible because various types of plastics exhibitvisual indications of being ready for forming, such as slight droppingor surface flattening.

According to the method of the present invention, while thethermoplastic sheet or blank 40 is being heated, a liquid materialhaving methyl methacrylate as a major constituent thereof is applied toa selected portion of the auxiliary member, in particular to the portionof the anchoring means within the periphery of model 24. As shown inFIG. 3, the liquid material is applied by means of a brush 44 orequivalent applicator such as a spatula to portions 32 of wire 30 and tothe corresponding portions 34 of wires 33. For example, one of theportions 32 of wire 30 shown in FIG. 3 has liquid material 46. Theliquid material has sufficient viscosity so that it clings to the wire,completely surrounding it, as illustrated in FIG. 6.

Material 46 is a synthetic polymerizable material of the rapid settingacrylic type, a major constituent of which is methyl methacrylate, andis commercially available under the designation cold cure acrylic. Theliquid material 46 may be compounded from one or more solid finelydivided polymers and one or more liquid polymerizable monomers, themonomer portion of the composition forming at least a partial solventfor the polymer portion.

The next step in the method of the present invention is applying theheated thermoplastic material 40 to model 24 and shaping the plasticmaterial to conform to the shape of the model. This is accomplished withmachine 10 of FIG. 1 by swinging lamp 20 to a standby position and thenmoving component 16 about the pivot of bracket 18 to a position shown inFIG. 4 whereupon a pressure seal is effected and then air under pressureis introduced from a passage 48 to force plastic blank 40 against model24 as shown in FIG. 4. When using a machine similar to machine 10 forforming a retainer from plastic material having a thickness of 1.5 to2.0 millimeters, the operating pressure should be about four to fivekillograms per square centimeter. As an alternative to applying positivepressure against blank 40, molding could be performed by suction fromthe surface of blank 40 adjacent mold 24 thereby requiring that anaperture be provided in model 24 for withdrawing air between blank 40and model 24. The plastic material is formed on model 24 in a mannerwhereby the portions 32 and 34 of wires 30 and 33, respectively, areembedded in the plastic material 40. Actually, other portions of thewires may be embedded in plastic 40 such as the portions contacting theteeth of model 24, but such excess plastic will be removed during asubsequent step. After the high pressure forming operation, the plasticis allowed to cool under pressure for an approximate time of at leasttwo minutes.

The component 16 of machine 10 then is removed from the model 24 andmoved back to the position of FIG. 1 whereupon model 24 and plastic 40can be removed from receptacle 12 by hand. The plastic 40 containingembedded wires 30, 33 then is separated from model 24 by hand using agentle finger force and working around the model. If themodel wasproperly positioned in receptacle 12 and the undercut surfaces properlymasked or isolated with the lead pellets 38, the plastic will releaseeasily. A suitable cutting tool is used to trim the excess plastic byfollowing the impression made therein by the inner surfaces of theteeth. When trimming is done near wires 30, 34 it should be done only upa distance of about one-half millimeter from the wires, and then theremaining plastic can be broken easily to free the wire. The portion ofthe finished product which was in contact with mold 24 is coated with aresinous liquid in the form of acrylic resin solution marketed under thetradename Acrypol by Scheu- Dental of West Germany. This imparts a highgloss finish to the surface. This same liquid can be applied to the edgeof the product for finishing the same.

In the method of the present invention liquid material 46 serves as anintermediary between the relatively hot plastic material 40 and therelatively cold auxiliaries such as anchoring wires 30, 33 duringtheforming and shaping operation. As the heated plastic material 40 isapplied to wires 30, 34 and mold 24, the liquid material serves as avehicle to enable the plastic material to wrap itself around or surroundthe wires during the forming and shaping operation. The liquid materialand the plastic have a common basis or characteristic in that bothinclude methyl methacrylate in a substantial amount. As a result, theselected portions of the wires 30, 34 are completely embedded in theplastic material. The liquid material is applied to the accessorieswhile the plastic material 40 is being heated by machine 10, and it isimportant that the heated plastic material be applied to model 24 andthe auxiliaries before the liquid material begins to cure. The fact thatwires 30, 33 can be completely embedded in a relatively thin, singlesheet of plastic material provides a relatively strong and effectivedevice which is made by a method which is performed relatively quicklyand easily. The pellets 38 of lead or similar relatively dense materialnot only protect or mask those surfaces of model 24 to which plastic isnot to be applied so as to facilitate separation of the model andplastic but also have the advantagethat they can be used repeatedly.

FIG. 5 shows a finished device 50 formed by the method of the presentinvention. Device 50 is known inthe art as a retainer and isusedpassively for retaining the teeth positions or actively'formodifying the position of certain teeth. The shape of plastic bodyportion 40 matches the palate of the patient and the edge 52 of portion40 matches the contour of the teeth. The device 50 is held in place bythe natural adhesion between the device and the palate with theinterposition of a film of saliva. The auxiliaries such as wires 30, 33apply force to the teeth by virtue of their configuration andresiliency.

The device 50 formed by the method of the present invention has arelatively thin plastic body portion 40 which is unitary or integral. Byway of example, the thickness of plastic body portion 40 is in the rangeof from about 2.0 millimeters 'to about 0.5 millimeters depending uponthe original thickness of the particular sheet or blank used. The endsof the wires 30, 33 are effectively secured in plastic body 40 in thatthey are completely embedded therein. The device 50 in having arelatively thin and unitary plastic body portion wears comfortably andis relatively economical to manufacture since the method can beperformed quickly and easily. The device 50 functions effectively andhas a relatively long wear life due to the embedding of wires 30, 33 inplastic body portion 40. While the method of the present invention hasbeen described in connection with forming device 50 it can be extendedto forming retainers having screws, separators, springs or nametags inthe plastic body portion in which case the liquid material is applied tothese accessories in the same manner as it is applied to the anchoringwires.

It is therefore apparent that the present invention accomplishes itsintended objects. While a single embodiment of the present invention hasbeen described in detail, this is for the purpose of illustration, notlimitation.

What is claimed is:

1. A method of making a dental appliance comprismg:

a. providing a dental model formed from an impression taken from themouth of a patient;

b. positioning an auxiliary member on said model;

0. supporting said model;

d. applying a liquid material having methyl methacrylate as a majorconstituent thereof to a selected portion of said auxiliary member;

e. applying heated thermoplastic material to said model and shaping saidplastic material to conform to'the shape of said model; and

f. cooling said plastic material.

2. A method according to claim 1, wherein said auxiliary membercomprises an anchoring wire which is positioned so that a portion isadjacent the palatal portion of said model and wherein said' liquidmaterial is applied to said portion of said wire adjacent said modelpalatal portion.

3. A method according to claim 2, wherein a plurality of anchoring wiresare positioned on said model, each wire having aportion adjacent thepalatal portion of said model, and wherein said liquid material isapplied to each of said wire portions adjacent said model palatalportion.

4. A method according to claim 1, wherein said model is supported byplacing a plurality'of relatively small pellets of a relatively densematerial against surfaces of said model not to receive plastic.

5. A method according to claim 4, wherein said pel lets are of lead. j

-6. A method according to claim 4, wherein said model is placed in anopen top receptacle with the top edge of the teeth of said modelapproximately flush with the top of said receptacle and wherein saidpellets are placed in said receptacle around said model and below thetop edge of the teeth thereof.

7. A method according to claim 1, wherein said heated plastic materialis applied to said model before said liquid material on said auxiliarymember begins to cure.

8. A method according to claim 1, wherein said thermoplastic materialhas methyl methacrylate as a major constituent thereof.

9. A method according to claim 1, wherein said thermoplastic material isapplied to said model and shaped in a manner embedding said selectedportion of said auxiliary member in said plastic material.

10. A method according to claim 1, further including separating theresulting product from the model and removing any excess plastictherefrom.

11. A method according to claim 10, further including applying a coatingof a resinous liquid to the surface of said product which was in contactwith said model to finish said surface.

12. A dental appliance obtained by the method of claiml.

2. A method according to claim 1, wherein said auxiliary membercomprises an anchoring wire which is positioned so that a portion isadjacent the palatal portion of said model and wherein said liquidmaterial is applied to said portion of said wire adjacent said modelpalatal portion.
 3. A method according to claim 2, wherein a pluralityof anchoring wires are positioned on said model, each wire having aportion adjacent the palatal portion of said model, and wherein saidliquid material is applied to each of said wire portions adjacent saidmodel palatal portion.
 4. A method according to claim 1, wherein saidmodel is supported by placing a plurality of relatively small pellets ofa relatively dense material against surfaces of said model not toreceive plastic.
 5. A method according to claim 4, wherein said pelletsare of lead.
 6. A method according to claim 4, wherein said model isplaced in an open top receptacle with the top edge of the teeth of saidmodel approximately flush with the top of said receptacle and whereinsaid pellets are placed in said receptacle around said model and belowthe top edge of the teeth thereof.
 7. A method according to claim 1,wherein said heated plastic material is applied to said model beforesaid liquid material on said auxiliary member begins to cure.
 8. Amethod according to claim 1, wherein said thermoplastic material hasmethyl methacrylate as a major constituent thereof.
 9. A methodaccording to claim 1, wherein said thermoplastic material is applied tosaid model and shaped in a manner embedding said selected portion ofsaid auxiliary member in said plastic material.
 10. A method accordingto claim 1, further including separating the resulting product from themodel and removing any excess plastic therefrom.
 11. A method accordingto claim 10, further including applying a coating of a resinous liquidto the surface of said product which was in contact with said model tofinish said surface.
 12. A dental appliance obtained by the method ofclaim 1.